1. Field of Invention
The present invention relates primarily to subsurface drainage systems of water or other fluids from soil or other materials, and more specifically to soil drainage systems that provide a new and revolutionary way to extract water or other fluids from soil for a wide variety of applications such as highways, buildings, retaining walls, water wells, slope stabilization, landfills, and farm grounds at low cost and high efficiency.
2. Description of Prior Art
Water drainage from soils is a very critical problem that relates to many important applications that affect our everyday life. Lack of proper drainage of undesirable water from soil exacts a tremendous cost from our economy while extracting usable water from water wells is so essential for living in many areas around the nation and the world. By far the largest application involves our national road and highway systems. Here, in the United States, poor drainage, especially in the winter when freezing and thawing frequently occur, leads to deterioration and failure of pavements, the cost of which is measured in the billions of dollars annually. Lack of soil drainage under homes and buildings causes heavy damage to the foundations and seepage of water and moisture to subsurface building space. This water or moisture damages furniture as well as the structure and creates fungi like mildew, extremely harmful to our health. Lack of drainage behind retaining walls is a major cause of wall failures. Lack of good interior drainage in sloped ground is a major cause of landslides when the ground becomes saturated after heavy precipitation. Drilling and developing water wells for the purpose of extracting water from the ground for domestic use or other uses (purposes) is quite expensive and time consuming. Properly draining farm grounds while controlling the water table and preventing soil loss and erosion is essential for successful farming by adding productive acreage to farms that otherwise will be wasted. Efficient soil drainage can also be a very important tool in cleaning (decontaminating) soils that are contaminated with salts, other chemicals, and certain hazardous wastes.
To improve/establish soil drainage in the above stated applications, a number of approaches are in use in some, while others have yet to be established.
Road and Highway Applications
To improve soil drainage, a number of approaches are in use. These applications include the use of sand, gravel, and other permeable materials as well as a variety of artificial under-surface drains (henceforth referred to simply as drains). The most common drains and their limitations or disadvantages are the following:    (i) The perforated, corrugated, plastic pipe with or without a sock which is a sleeve made from an appropriate filter cloth material. The disadvantages of this system are that the corrugations impede water flow due to induced turbulence, collected precipitates, and provide ideal rodent nesting and infestation environment. (The pipe with a sock clogs up easily) This is especially critical for pavements where the hydraulic gradient (i.e. the slope) is normally quite small and the need to quickly eliminate the water is great. This drain is also difficult to flush clean because the obstructions anchor themselves in the corrugations. Once put in place into dug trenches, the drain requires back filling with granular material to be effective, an added cost. Without granular backfill, drainage is very limited to the small areas radial to the perforations. Also, due to its thin construction, it suffers from low compressive strength and collapse of the pipe from vehicular load is quite common.    (ii) The so-called “French drain”, consists of a trench whose walls are lined (or unlined) with a filter fabric and backfilled with sand and/or gravel. It requires a relatively large trench, which means large trench excavation and large amounts of granular backfill material at high cost. This drain suffers from low flow velocity which prevents the removal of water in a timely manner. When lined with a filter fabric, the installation of this drain becomes more labor intensive. The added material and labor increases the cost significantly.    (iii) The geocomposite edge drain, or strip drain, which consists of a cuspate or dimpled plastic skeleton core of a nominal width, usually 24 inches maximum and wrapped all around with geotextile filter fabric. This drain is installed in a narrow trench along the edge of the pavement or behind retaining walls. This drain suffers from low core capacity and the hindrance of longitudinal flow (velocity) by the manner in which the core is constructed.Homes and Building Applications
Before pouring the concrete for basement floors, trenches are usually dug around and across the basement footprint in such a formation so that the final drainage of water ends up at the sump pump pits. Perforated corrugated pipe drains are then placed in the trenches and are connected in such ways to outlet in the sump pump pits. The trenches are then backfilled with crushed rock or gravel. Most of the time, filter fabric lining of the ditches is omitted to save labor and material. As a result, loss of fine soil and cavitations under the floor slabs can arise with the passage of time and produce loss of support.
Retaining Wall Applications
In retaining wall design and construction, it is essential to reduce or eliminate the water pressure build-up behind the wall. Failure to do so may increase the design pressure load by a factor of 2 or more. In routine retaining wall construction, where construction starts at the bottom, it is relatively easy to design and put into place a good drainage system. The collector perforated pipe is either wrapped in a sock, which is a sleeve made from an appropriate woven filter cloth and backfilled with granular material, or a bare perforated pipe placed inside a finite volume of gravel which is then wrapped or encapsulated with a geotextile filter cloth. In the first case, the flow into the pipe is through the woven filter material immediately across from the pipe perforations; that flow, small to start with, is further reduced significantly by any fine soil that clogs those areas of the filter cloth. In the second case, the safety of the drainage flow is more assured, however at higher material and labor costs. In some of the more complex retaining wall construction, what is called “top down construction”, retaining walls like slurry walls, sheet pile walls, and tangent pile walls often have no drainage provisions behind these walls. Yet, these walls, by virtue of the terrain they are in, can benefit greatly from a good drainage system.
Because the ground water is trapped behind the wall, most of the time they are designed for more than twice the design pressure load that a well drained wall is designed for. This means a much higher cost for material and labor and a shortened design life.
Landslide Mitigation
Ground slopes, like the side of a hill, are many times prone to very damaging landslides such as what happens in California, the Northwest United States and elsewhere. This is especially true during periods of heavy precipitation when the ground gets saturated and the build up of pore water pressure in the soil increases the driving forces and reduces the resisting forces, thus resulting in landslides that can destroy buildings and expensive homes that are built on these hills, and can cause blocking of roads and highways that are built on the sides of the hills, even rendering them impassable. This condition can be remedied through the use of so-called “horizontal drains” that are installed at strategic locations deep into the side of the hill or sloping ground. At present, most of these situations go without corrective treatments and spectacular failures take place. The current state of the art technology for horizontal drains employ steel or PVC pipes with evenly spaced slots or perforations and may be fitted with a knitted tubular geotextile sleeve or a simple wrapping of geotextile sheet, though this is not recommended in most situations because the sleeve can inhibit the effectiveness of cleaning and thus promote clogging. The major downfall of these pipes is that they do not effectively drain large amounts of water quickly enough.
Water Wells and Well Points
Water wells are developed and used to extract water from the ground as a valuable resource for domestic consumption and other uses such as for dewatering excavations for structural foundations to facilitate construction below grade. Wells are used in construction when water flow is rather large, while well points, basically small diameter wells, are used in tight soils where the water flow yield is expected to be small. Both water wells and well points employ a metal or plastic intake pipe, a metal screen (the slotted part of the casing or for aquifers that have sand and gravel, either continuous), and a sand filter pack. Slotted screens are made of wire or plastic wrapped around a series of vertical rods, or slotted pipe screens which have very small open areas of machine cut slots into the casing at set distances. As can be implied, the process of installing the well intake screen and filter is difficult, time consuming, expensive, and may not give the most desirable results.
Farm Drains
Proper drainage of farm grounds while controlling loss of soil is essential for successful fanning because it adds productive acreage to farms that otherwise will be wasted because of excessive moisture in the soil or loss of soil. The drain of choice used in this application has been the tile drain or the perforated corrugated pipe. The tile drains come in short lengths of pipe with open joints set next to each other in a ditch and buried in the ground. They are day-lighted at a low point to drain in a drainage ditch or a creek. This drain suffers from limited drainage and major erosion and loss of valuable soil due to piping that occurs through the joints. Corrugated perforated plastic pipe is similarly used, first buried and then set in sand in trenches. This is complicated and expensive to use a good graduated granular filter in the trench around the pipe.
Decontamination of Soil and Farm Irrigation
Good soil drainage can be a very important tool in decontaminating certain soils that are contaminated with residual chemicals, like some of the low lying farm land in San Joaquin Valley in California. This problem has been neglected so far, thus losing to contamination very valuable land. Also controlling optimum water table for different crops in irrigated semi-arid farms in California and elsewhere is greatly enhanced through a good drainage system that controls the depth of the water table.
Landfills
Collecting and removing leachate from landfills is a critical and important environmental concern. A good drainage system employing large, horizontal drains made of plastics with inert properties is a very important tool to accomplish the job of safely collecting and removing leachate to reduce possible groundwater contamination.